/*
Copyright 2017 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

*/

package auth

import (
	"crypto/tls"
	"encoding/json"
	"net/http"
	"net/url"
	"strings"

	"github.com/gravitational/teleport"
	"github.com/gravitational/teleport/lib"
	"github.com/gravitational/teleport/lib/httplib"
	"github.com/gravitational/teleport/lib/services"
	"github.com/gravitational/teleport/lib/tlsca"

	"github.com/gravitational/roundtrip"
	"github.com/gravitational/trace"
)

// UpsertTrustedCluster creates or toggles a Trusted Cluster relationship.
func (a *AuthServer) UpsertTrustedCluster(trustedCluster services.TrustedCluster) (services.TrustedCluster, error) {
	var exists bool

	// it is recommended to omit trusted cluster name, because
	// it will be always set to the cluster name as set by the cluster
	var existingCluster services.TrustedCluster
	var err error
	if trustedCluster.GetName() != "" {
		existingCluster, err = a.Presence.GetTrustedCluster(trustedCluster.GetName())
		if err == nil {
			exists = true
		}
	}

	enable := trustedCluster.GetEnabled()

	// if the trusted cluster already exists in the backend, make sure it's a
	// valid state change client is trying to make
	if exists == true {
		err := existingCluster.CanChangeStateTo(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}
	}

	// change state
	switch {
	case exists == true && enable == true:
		log.Debugf("Enabling existing Trusted Cluster relationship.")

		err := a.activateCertAuthority(trustedCluster)
		if err != nil {
			if trace.IsNotFound(err) {
				return nil, trace.BadParameter("enable only supported for Trusted Clusters created with Teleport 2.3 and above")
			}
			return nil, trace.Wrap(err)
		}

		err = a.createReverseTunnel(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}
	case exists == true && enable == false:
		log.Debugf("Disabling existing Trusted Cluster relationship.")

		err := a.deactivateCertAuthority(trustedCluster)
		if err != nil {
			if trace.IsNotFound(err) {
				return nil, trace.BadParameter("enable only supported for Trusted Clusters created with Teleport 2.3 and above")
			}
			return nil, trace.Wrap(err)
		}

		err = a.DeleteReverseTunnel(trustedCluster.GetName())
		if err != nil {
			return nil, trace.Wrap(err)
		}
	case exists == false && enable == true:
		log.Debugf("Creating enabled Trusted Cluster relationship.")

		if err := a.checkLocalRoles(trustedCluster.GetRoleMap()); err != nil {
			return nil, trace.Wrap(err)
		}

		remoteCAs, err := a.establishTrust(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		// force name of the trusted cluster resource
		// to be equal to the name of the remote cluster it is connecting to
		trustedCluster.SetName(remoteCAs[0].GetClusterName())

		err = a.addCertAuthorities(trustedCluster, remoteCAs)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		err = a.createReverseTunnel(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}

	case exists == false && enable == false:
		log.Debugf("Creating disabled Trusted Cluster relationship.")

		if err := a.checkLocalRoles(trustedCluster.GetRoleMap()); err != nil {
			return nil, trace.Wrap(err)
		}

		remoteCAs, err := a.establishTrust(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		// force name to the name of the trusted cluster
		trustedCluster.SetName(remoteCAs[0].GetClusterName())

		err = a.addCertAuthorities(trustedCluster, remoteCAs)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		err = a.deactivateCertAuthority(trustedCluster)
		if err != nil {
			return nil, trace.Wrap(err)
		}
	}
	return a.Presence.UpsertTrustedCluster(trustedCluster)
}

func (a *AuthServer) checkLocalRoles(roleMap services.RoleMap) error {
	for _, mapping := range roleMap {
		for _, localRole := range mapping.Local {
			_, err := a.GetRole(localRole)
			if err != nil {
				if trace.IsNotFound(err) {
					return trace.NotFound("a role %q referenced in a mapping %v:%v is not defined", localRole, mapping.Remote, mapping.Local)
				}
				return trace.Wrap(err)
			}
		}
	}
	return nil
}

// DeleteTrustedCluster removes services.CertAuthority, services.ReverseTunnel,
// and services.TrustedCluster resources.
func (a *AuthServer) DeleteTrustedCluster(name string) error {
	err := a.DeleteCertAuthority(services.CertAuthID{Type: services.HostCA, DomainName: name})
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}

	err = a.DeleteCertAuthority(services.CertAuthID{Type: services.UserCA, DomainName: name})
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}

	err = a.DeleteReverseTunnel(name)
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}

	err = a.Presence.DeleteTrustedCluster(name)
	if err != nil {
		return trace.Wrap(err)
	}

	return nil
}

func (a *AuthServer) establishTrust(trustedCluster services.TrustedCluster) ([]services.CertAuthority, error) {
	var localCertAuthorities []services.CertAuthority

	domainName, err := a.GetDomainName()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// get a list of certificate authorities for this auth server
	allLocalCAs, err := a.GetCertAuthorities(services.HostCA, false)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	for _, lca := range allLocalCAs {
		if lca.GetClusterName() == domainName {
			localCertAuthorities = append(localCertAuthorities, lca)
		}
	}

	// create a request to validate a trusted cluster (token and local certificate authorities)
	validateRequest := ValidateTrustedClusterRequest{
		Token: trustedCluster.GetToken(),
		CAs:   localCertAuthorities,
	}

	// log the local certificate authorities that we are sending
	log.Debugf("Sending validate request; token=%v, CAs=%v", validateRequest.Token, validateRequest.CAs)

	// send the request to the remote auth server via the proxy
	validateResponse, err := a.sendValidateRequestToProxy(trustedCluster.GetProxyAddress(), &validateRequest)
	if err != nil {
		log.Error(err)
		if strings.Contains(err.Error(), "x509") {
			return nil, trace.AccessDenied("the trusted cluster uses misconfigured HTTP/TLS certificate.")
		}
		return nil, trace.Wrap(err)
	}

	// log the remote certificate authorities we are adding
	log.Debugf("Received validate response; CAs=%v", validateResponse.CAs)

	for _, ca := range validateResponse.CAs {
		for _, keyPair := range ca.GetTLSKeyPairs() {
			cert, err := tlsca.ParseCertificatePEM(keyPair.Cert)
			if err != nil {
				return nil, trace.Wrap(err)
			}
			remoteClusterName, err := tlsca.ClusterName(cert.Subject)
			if err != nil {
				return nil, trace.Wrap(err)
			}
			if remoteClusterName == domainName {
				return nil, trace.BadParameter("remote cluster name can not be the same as local cluster name")
			}
			// TODO(klizhentas) in 2.5.0 prohibit adding trusted cluster resource name
			// different from cluster name (we had no way of checking this before x509,
			// because SSH CA was a public key, not a cert with metadata)
		}
	}

	return validateResponse.CAs, nil
}

func (a *AuthServer) addCertAuthorities(trustedCluster services.TrustedCluster, remoteCAs []services.CertAuthority) error {
	// the remote auth server has verified our token. add the
	// remote certificate authority to our backend
	for _, remoteCertAuthority := range remoteCAs {
		// change the name of the remote ca to the name of the trusted cluster
		remoteCertAuthority.SetName(trustedCluster.GetName())

		// wipe out roles sent from the remote cluster and set roles from the trusted cluster
		remoteCertAuthority.SetRoles(nil)
		if remoteCertAuthority.GetType() == services.UserCA {
			for _, r := range trustedCluster.GetRoles() {
				remoteCertAuthority.AddRole(r)
			}
			remoteCertAuthority.SetRoleMap(trustedCluster.GetRoleMap())
		}

		// we use create here instead of upsert to prevent people from wiping out
		// their own ca if it has the same name as the remote ca
		err := a.CreateCertAuthority(remoteCertAuthority)
		if err != nil {
			return trace.Wrap(err)
		}
	}

	return nil
}

// DeleteRemoteCluster deletes remote cluster resource, all certificate authorities
// associated with it
func (a *AuthServer) DeleteRemoteCluster(clusterName string) error {
	// To make sure remote cluster exists - to protect against random
	// clusterName requests (e.g. when clusterName is set to local cluster name)
	_, err := a.Presence.GetRemoteCluster(clusterName)
	if err != nil {
		return trace.Wrap(err)
	}
	// delete cert authorities associated with the cluster
	err = a.DeleteCertAuthority(services.CertAuthID{
		Type:       services.HostCA,
		DomainName: clusterName,
	})
	if err != nil {
		// this method could have succeeded on the first call,
		// but then if the remote cluster resource could not be deleted
		// it would be impossible to delete the cluster after then
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}
	// there should be no User CA in trusted clusters on the main cluster side
	// per standard automation but clean up just in case
	err = a.DeleteCertAuthority(services.CertAuthID{
		Type:       services.UserCA,
		DomainName: clusterName,
	})
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}
	return a.Presence.DeleteRemoteCluster(clusterName)
}

// GetRemoteCluster returns remote cluster by name
func (a *AuthServer) GetRemoteCluster(clusterName string) (services.RemoteCluster, error) {
	// To make sure remote cluster exists - to protect against random
	// clusterName requests (e.g. when clusterName is set to local cluster name)
	remoteCluster, err := a.Presence.GetRemoteCluster(clusterName)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	if err := a.updateRemoteClusterStatus(remoteCluster); err != nil {
		return nil, trace.Wrap(err)
	}
	return remoteCluster, nil
}

func (a *AuthServer) updateRemoteClusterStatus(remoteCluster services.RemoteCluster) error {
	// fetch tunnel connections for the cluster to update runtime status
	connections, err := a.GetTunnelConnections(remoteCluster.GetName())
	if err != nil {
		return trace.Wrap(err)
	}
	remoteCluster.SetConnectionStatus(teleport.RemoteClusterStatusOffline)
	lastConn, err := services.LatestTunnelConnection(connections)
	if err == nil {
		remoteCluster.SetConnectionStatus(services.TunnelConnectionStatus(a.clock, lastConn))
		remoteCluster.SetLastHeartbeat(lastConn.GetLastHeartbeat())
	}
	return nil
}

// GetRemoteClusters returns remote clusters with udpated statuses
func (a *AuthServer) GetRemoteClusters() ([]services.RemoteCluster, error) {
	// To make sure remote cluster exists - to protect against random
	// clusterName requests (e.g. when clusterName is set to local cluster name)
	remoteClusters, err := a.Presence.GetRemoteClusters()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	for i := range remoteClusters {
		if err := a.updateRemoteClusterStatus(remoteClusters[i]); err != nil {
			return nil, trace.Wrap(err)
		}
	}
	return remoteClusters, nil
}

func (a *AuthServer) validateTrustedCluster(validateRequest *ValidateTrustedClusterRequest) (*ValidateTrustedClusterResponse, error) {
	domainName, err := a.GetDomainName()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// validate that we generated the token
	err = a.validateTrustedClusterToken(validateRequest.Token)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// log the remote certificate authorities we are adding
	log.Debugf("Received validate request: token=%v, CAs=%v", validateRequest.Token, validateRequest.CAs)

	// add remote cluster resource to keep track of the remote cluster
	var remoteClusterName string
	for _, certAuthority := range validateRequest.CAs {
		// don't add a ca with the same as as local cluster name
		if certAuthority.GetName() == domainName {
			return nil, trace.AccessDenied("remote certificate authority has same name as cluster certificate authority: %v", domainName)
		}
		remoteClusterName = certAuthority.GetName()
	}
	remoteCluster, err := services.NewRemoteCluster(remoteClusterName)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	err = a.CreateRemoteCluster(remoteCluster)
	if err != nil {
		if !trace.IsAlreadyExists(err) {
			return nil, trace.Wrap(err)
		}
	}

	// token has been validated, upsert the given certificate authority
	for _, certAuthority := range validateRequest.CAs {
		err = a.UpsertCertAuthority(certAuthority)
		if err != nil {
			return nil, trace.Wrap(err)
		}
	}

	// export our certificate authority and return it to the cluster
	validateResponse := ValidateTrustedClusterResponse{
		CAs: []services.CertAuthority{},
	}
	for _, caType := range []services.CertAuthType{services.HostCA, services.UserCA} {
		certAuthorities, err := a.GetCertAuthorities(caType, false)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		for _, certAuthority := range certAuthorities {
			if certAuthority.GetClusterName() == domainName {
				validateResponse.CAs = append(validateResponse.CAs, certAuthority)
			}
		}
	}

	// log the local certificate authorities we are sending
	log.Debugf("Sending validate response: CAs=%v", validateResponse.CAs)

	return &validateResponse, nil
}

func (a *AuthServer) validateTrustedClusterToken(token string) error {
	roles, err := a.ValidateToken(token)
	if err != nil {
		return trace.AccessDenied("the remote server denied access: invalid cluster token")
	}

	if !roles.Include(teleport.RoleTrustedCluster) && !roles.Include(teleport.LegacyClusterTokenType) {
		return trace.AccessDenied("role does not match")
	}

	return nil
}

func (s *AuthServer) sendValidateRequestToProxy(host string, validateRequest *ValidateTrustedClusterRequest) (*ValidateTrustedClusterResponse, error) {
	proxyAddr := url.URL{
		Scheme: "https",
		Host:   host,
	}

	var opts []roundtrip.ClientParam

	if lib.IsInsecureDevMode() {
		log.Warn("The setting insecureSkipVerify is used to communicate with proxy. Make sure you intend to run Teleport in insecure mode!")

		// get the default transport (so we can get the proxy from environment)
		// but disable tls certificate checking.
		tr, ok := http.DefaultTransport.(*http.Transport)
		if !ok {
			return nil, trace.BadParameter("unable to get default transport")
		}
		tr.TLSClientConfig = &tls.Config{InsecureSkipVerify: true}

		insecureWebClient := &http.Client{
			Transport: tr,
		}
		opts = append(opts, roundtrip.HTTPClient(insecureWebClient))
	}

	clt, err := roundtrip.NewClient(proxyAddr.String(), teleport.WebAPIVersion, opts...)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	validateRequestRaw, err := validateRequest.ToRaw()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	out, err := httplib.ConvertResponse(clt.PostJSON(clt.Endpoint("webapi", "trustedclusters", "validate"), validateRequestRaw))
	if err != nil {
		return nil, trace.Wrap(err)
	}

	var validateResponseRaw *ValidateTrustedClusterResponseRaw
	err = json.Unmarshal(out.Bytes(), &validateResponseRaw)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	validateResponse, err := validateResponseRaw.ToNative()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	return validateResponse, nil
}

type ValidateTrustedClusterRequest struct {
	Token string                   `json:"token"`
	CAs   []services.CertAuthority `json:"certificate_authorities"`
}

func (v *ValidateTrustedClusterRequest) ToRaw() (*ValidateTrustedClusterRequestRaw, error) {
	cas := [][]byte{}

	for _, certAuthority := range v.CAs {
		data, err := services.GetCertAuthorityMarshaler().MarshalCertAuthority(certAuthority)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		cas = append(cas, data)
	}

	return &ValidateTrustedClusterRequestRaw{
		Token: v.Token,
		CAs:   cas,
	}, nil
}

type ValidateTrustedClusterRequestRaw struct {
	Token string   `json:"token"`
	CAs   [][]byte `json:"certificate_authorities"`
}

func (v *ValidateTrustedClusterRequestRaw) ToNative() (*ValidateTrustedClusterRequest, error) {
	cas := []services.CertAuthority{}

	for _, rawCertAuthority := range v.CAs {
		certAuthority, err := services.GetCertAuthorityMarshaler().UnmarshalCertAuthority(rawCertAuthority)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		cas = append(cas, certAuthority)
	}

	return &ValidateTrustedClusterRequest{
		Token: v.Token,
		CAs:   cas,
	}, nil
}

type ValidateTrustedClusterResponse struct {
	CAs []services.CertAuthority `json:"certificate_authorities"`
}

func (v *ValidateTrustedClusterResponse) ToRaw() (*ValidateTrustedClusterResponseRaw, error) {
	cas := [][]byte{}

	for _, certAuthority := range v.CAs {
		data, err := services.GetCertAuthorityMarshaler().MarshalCertAuthority(certAuthority)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		cas = append(cas, data)
	}

	return &ValidateTrustedClusterResponseRaw{
		CAs: cas,
	}, nil
}

type ValidateTrustedClusterResponseRaw struct {
	CAs [][]byte `json:"certificate_authorities"`
}

func (v *ValidateTrustedClusterResponseRaw) ToNative() (*ValidateTrustedClusterResponse, error) {
	cas := []services.CertAuthority{}

	for _, rawCertAuthority := range v.CAs {
		certAuthority, err := services.GetCertAuthorityMarshaler().UnmarshalCertAuthority(rawCertAuthority)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		cas = append(cas, certAuthority)
	}

	return &ValidateTrustedClusterResponse{
		CAs: cas,
	}, nil
}

// activateCertAuthority will activate both the user and host certificate
// authority given in the services.TrustedCluster resource.
func (a *AuthServer) activateCertAuthority(t services.TrustedCluster) error {
	err := a.ActivateCertAuthority(services.CertAuthID{Type: services.UserCA, DomainName: t.GetName()})
	if err != nil {
		return trace.Wrap(err)
	}

	return trace.Wrap(a.ActivateCertAuthority(services.CertAuthID{Type: services.HostCA, DomainName: t.GetName()}))
}

// deactivateCertAuthority will deactivate both the user and host certificate
// authority given in the services.TrustedCluster resource.
func (a *AuthServer) deactivateCertAuthority(t services.TrustedCluster) error {
	err := a.DeactivateCertAuthority(services.CertAuthID{Type: services.UserCA, DomainName: t.GetName()})
	if err != nil {
		return trace.Wrap(err)
	}

	return trace.Wrap(a.DeactivateCertAuthority(services.CertAuthID{Type: services.HostCA, DomainName: t.GetName()}))
}

// createReverseTunnel will create a services.ReverseTunnel givenin the
// services.TrustedCluster resource.
func (a *AuthServer) createReverseTunnel(t services.TrustedCluster) error {
	reverseTunnel := services.NewReverseTunnel(
		t.GetName(),
		[]string{t.GetReverseTunnelAddress()},
	)
	return trace.Wrap(a.UpsertReverseTunnel(reverseTunnel))
}
